Method of electrically melting metals and in an electric furnace



Oct. 9 1923. 1,469,817

I. RENNERFELT METHOD OF ELECTRICALLY MELTING METALS AND IN AN ELECTRIC FURNACE Filed June 16. 1921 Wz'fnesses: In veni'or:

Patented Oct. 9, 1923.

UNITED STATES IVAR RENNERFELT, OF DJURSHOLM, SWEDEN.

METHOD or ELECTRICALLY MELTING METALS Aim IN AN nLncrn-xorunnaon.

Application filed June 16, 1921. Serial No. 478,095.

To all whom it may concern:

Be it known that 1, Ivan RENNERrEI/r, a citizen of the Kingdom of Sweden, and resident of Djursholm, in the county of Stock holm Lan and Kingdom of Sweden, have invented a certain new and useful Improvement in Methodsof Electrically Melting Metals and in an Electric Furnace (for which Ifiled application inSweden, Oct. 22, 1919), of which the following is a specification.

My invention relates to a certain im proved method of electrically meltin metals and especially iron and steel. t 5 relates also to an electric furnace, which is Well adapted to be used in connection with the method referred to. The objects of my invention are, first, to disclose a method for meltin economically a large quantity of metal with a comparatively small power,

the method being especially characterized by this, that the melting time is very long, in

most cases preferably close to 24 hours,

second, to disclose how an electric furnace 25 should be built to permit the accumulation of a considerable quantity of electric energy without an excessive loss of kilowatthours and to facilitate storing a considerable quantity of liquid metal, for instance steel or pigiron, discharging it in a very short time; and, third, to provide means, which will make it possible to introduce electric melting on a large scale in the foundries making ordinary gray or malleable iron castings.

The nature ofthe work in such foundries requires that a big quantity of liquid iron shall be available at a certain time, generally in the afternoon. Usually the iron is melted in one or more cupola furnaces or open hearths, delivering the iron at a. certain practically constant rate of melting, the metal being taken to the moulds practically without stopping. If the number of cupolas is insufficient, or if their melting capacity is rather small, the time reqluired for pouring the iron into the moul s will be quite considerable, causing a very considerable loss of time, which could with advantage be used for moulding work. The present foundry practice, however, prevents this savin of time, because it is practically im possi le to carry on any moulding work after the pouring of the iron has once started filling the foundry with smoke and disturbances of many'kinds. It is, furthermore,w ell known, that generally no pouring is possible "during the regular time of moulding, and therefore the iron must be melted as quickly as possible after the moulding work is done. I

A mediumsiz ed foundry may use some 50 tons of iron daily. To melt this electrically would require about 20,000 kwhrs. For melting the iron in 5 hours not less than 4,000fkw. would have to be supplied. This is hardly possible, as the cost of installation would be rather high and also the cost of the energy on account of the very bad load factor. If,however, the melting is going on day and night at a constant rate the power required would be only about 1,000 kw., which would be much cheaper to provide. To lessen still more the electric power re quired it is possible to combine electric meltingwith cupola melting, keeping the electric melting going duringthe night, obtaining a specially. cheap rate for the energy, melting in the cupola during the day and storing the cupola iron in the electric accumulating and melting furnace. It is of course possible and generally also necessary to supply a certain'amount of power to the electric furnace to keep the iron hot, and, if desired, to overheat it. The combination of the cupola with the electric furnace is especially valuable in places, where the coke is cheap but the electric energy expensive.

It is obvious that the iron will be greatly improved by being accumulated and heated to a very high temperature in a preferably basic electric furnace. Not only will the amount of sulphur decrease, but the iron will also contain less gases and slag.

It is also possible to soften a hard iron and to make corrections regarding the amount of manganese, silicon and other elements. I

If melting simultaneously in the electric furnace and in the cupola the latter may be comparatively small, being kept at maximum melting output all the time, which will increase the efficienc and lessen the amount of coke as no coo ing off of the cupola lining will take place from one day to the other, as is now customary.

It is obvious that it also is a considerable improvement upon the general foundry practice to accumulate a large quantity of high grade iron, making it possible to cast very heavy pieces withgreat convenience.

The method disclosed in my invention means also another improvement upon the foundry practice by making it possible to postpone the pouring a certain time in the afternoon, if the moulding work should so require. It is also possible to tap the furnace for instance in the morning if re quired.

In order to successfully use the method of melting according to my invention the furnace should be carefully built along certain lines. The insulation against loss of heat must be most excellent. Consequently the geometrical shape best suited to all purposes would be that of a cylinder resting on earings, permitting it to be rotated for discharging as usual with mixers.

The charging openings should be quite few and of small size as no big objects, but only liquid iron or common pigiron bars will as a rule be charged into the furnace. The charging openings may conveniently be placed one in each end of the cylinder. The discharging openings should preferably be made as o dinary tapholes with or without means for closing, located in the ends of the hearth and preferably also one or more in the cylindrical wall. t is desirable to use several tapholes located at different places so as to permit several men to get iron in their handladles simultaneously, preventing the usual, undesirable crowding of moulders at the single taphole of the cupola or open hearth. The tapholes should be located on the same level and preferably above the highest level of a full charge of iron in the furnace. By having the tapholes above the level of charge it will be possible to keep the holes clear from freezing and-in good shape.

To withdraw the liquid iron through tap holes at the bottom of a furnace of the mixer type is practically impossible, because of the considerable head of the iron above the hole, which would cause a high tapping velocity of the iron on flowing out, causing also serious difficulties, if it should become necessary to close the taphole, after it has been opened. The end tapholes should be located close to the inside cylindrical wall to make it possible to discharge the whole charge through said holes.

To facilitate withdrawal of slag when necessary the charging openings in the ends 1 the hearth may be extended sideways so ar as to make the charge overflow to a certain degree, when the furnace is being rotcted, in this way causing the slag to be discharged.

To supply the electric energy into the inrneoe several electrodes may be arran ifi orcgect the hearth from above. if

usin only such electrodes, which are practicalTy vertical, when the furnace is in its normal melting position, the heat will be generated in the usual way by means of arcs in contact with the charge.

It is possible also to use electrodes entering through the sides at a certain convenient angle to the horizontal plane cooperating with each other or with vertical electrodes to form arcs burning above the surface of the iron.

The furnace may be rotated considerably to one or both sides in order to cause movements in the bath for mixing it thoroughly. By rotating the furnace new parts of the lining will be brou ht in contact with the bath gettin cooled by this, if hotter than the iron. otating the furnace in this way requires closing the discharge openings temporarily by suitable means or locating all the holes high enough to permit a considerable rotation without the contents flowing out.

\Vhen rotating the furnace for mixin or discharging the iron it may be practica to withdraw the electrodes from the interior keeping them suspended in the air above the furnace, as is well known in the electric furnace practice.

Under certain circumstances it may be de sirable when tapping the metal to make the furnace roll on horizontal beds instead of rotating it as previously described, but the last method will probably be used more often than the former.

On the accompanying drawing Fig. 1 shows a vertical section at zca= in Fig. 2, which is a top view of a furnace according to the present invention, provided with three vertical electrodes. Fig. 3 is a vertical section of a furnace having two or more sets of electrodes, each set consisting of two adjustable electrodes entering from opposite sides at about 5 angle from the horizontal plane. A third vertical electrode may be used as indicated by dotted lines.

On the drawing a cylindrical melting hearth is indicated by 1, roller bearings supporting the heanth b 2 and a charge of liquid metal by 3. lectric arcs are indicated by 4 and electrodes 5 project vertically into the hearth and other electrodes 6 may project into the hearth at a considerable ale to the vertical line. In the end wall or the furnace tapholes 7 are provided close to the inside cylindrical wall at convenient places on one or both sides of the hearth. To facilitate charging of cold or liquid metal openings 9 are rovided in the end wall, closed by tightly fitting doors 10.

The openings 9 may be extended wide enough to one or both sides to cause the lower comer to dip underneath the level of the charge so as to cause the slag or the charge itself to overflow when rotating the four hours.

' withdrawn from the hearth in the same manner as steel is tapped from a ladle provided with means for tapping through the bottom. v

I do not wish to limit myself to the exact shape of the furnacesfllustrated on the drawin as several modified forms are pos sible without departin from the scope of my invention. It woul for instance be possible to provide also bottom contacts as indicated by 11 for supplying electric energy to the charge without using arcs for generating the heat.

Having now fully'described my invention I claim and desire to secure by Letters Patent of the United States of America.

lfThe .method of melting a metal which consists in providing a carefull insulated electric furnace charging it gradually with metal at a certain rate extendin over nearly twenty-four hours time an causing the metal to melt by sup lying electric power at a rate, which is su clent to cover the loss of heat from the furnace and'to furnish the amount of heat required for melting slowly the uantity of metal intended to be discharged about once every twenty- 2. The method of melting a metal, which consists in providing a carefully insulated electric furnace and a cupola furnace charging the electric furnace adually withmetal at a certain rate exten ing over nearly a ing. suflicient 'in the electric furnace and to keep the twenty-four hours time, taking the metal in .liquid state from the cupola, keeping this melting continuously for nearly twenty-four keep the metal hot in the electric furnace, discharging it about once every twentyfour hours.

3. The method of melting a metal which consists in providing a carefully insulated electric furnace and a cupola furnace charging the electric furnace gradually with cold metal during the night and with liquid metal from the cupola at daytime supplywer to melt the cold charge liquid bath hot at daytime, discharging it in the afternoon.

4. In an electric furnace the combination of a preferably cylindricalmelting hearth with electrodes projecting. through the cylindrical side, means for lowering one side of the furnace and simultaneously lifting the opposite side, openings in the endwalls close 'to the inside surface of the cylindrical wall and'a charging opening in t e end wall, located'so as to cause a layer of slag on top of a charge of metal to overflow when lowering one side of the hearth sufliciently. 1

Si ned at Stockholm in the county of Stoc holm. Lan and State of Sweden this 21st day of May A. D. 1921.

IVAR RENNERFELT. Witnesses:

Em IVERSON, Wmnnn C. ERIKSON. 

